The USDOT number
FMCSA assigns a USDOT number when a company registers. Inspections, crashes, audits and the company’s registration details (Form MCS-150) are all recorded under it, and it stays the same when the company updates its information.
The MC number
An MC number is a docket number that comes with operating authority. For-hire carriers that move regulated freight interstate and freight brokers generally need operating authority. Freight forwarders receive FF numbers and Mexico-based carriers MX numbers.
Why some companies have only a USDOT number
A private carrier that moves only its own goods, or a carrier that operates only within one state, can need a USDOT number without needing operating authority. One USDOT number can also hold more than one docket, for example a carrier authority and a broker authority.
Checking both
When you verify a company, check both: the USDOT status shows whether its registration is active, and the docket status shows whether its operating authority is active.
Related: USDOT number lookup · MC number lookup